Essential Stages of Drinking Water Treatment and Purification

Regulating Raw Water Flow and Reagent Dosing

The drinking water treatment process begins with the entry of raw water, regulated by a level control valve. The flow rate is adjusted using a series of fixed-section gates. Reagents are then added using a rapid agitator.

Essential Reagents in Water Treatment

The primary chemicals used in the initial stages include:

• Coagulant

  A substance that promotes the separation of water-insoluble phases through sedimentation. Coagulants destabilize suspended matter by altering the electrically charged ionic colloidal layer surrounding these particles. The most commonly used coagulants are iron salts and aluminum salts.

• Flocculant

  A chemical that binds suspended solids together, causing them to precipitate. Flocculants often consist of combined alum salts, typically including aluminum sulfate or ammonium aluminum sulfate.

• pH Corrector

  Used to regulate the water's pH level using strong acids or strong bases, ensuring optimal conditions for coagulation and disinfection.

Flocculation and Sedimentation

After leaving the agitator, the water is subjected to flocculation, a process that encourages the coalescence of destabilized particles, creating larger aggregates called flocs. This water then flows slowly through settling tanks (sedimentation basins), where the flocs are deposited on the bottom, forming a sludge blanket. This sludge is subsequently treated and properly disposed of.

Water Filtration

Once decanted, the water passes through a bed of sand (or other filter media) where remaining fine particles are trapped. This process ensures the water reaches the final stages with high clarity.

Final Disinfection

The water undergoes final chlorination to ensure a proper residual chlorine load, guaranteeing microbiological safety throughout the distribution network.

Sludge Treatment and Disposal

The process generates significant volumes of sludge that require treatment and conditioning. Following treatment, the sludge is transferred and deposited as waste in an approved landfill.

Methods of Drinking Water Purification

1. Chlorination

Chlorination involves the automatic dosing, measurement, and control of free chlorine. A target value (setpoint) is established, which must remain stable over time, managed with the help of a computer and a dosing pump. The system also controls the pH; if the pH is too high, hydrochloric acid (HCl) may be added to maintain the effectiveness of the chlorine.

Besides chlorine compounds (such as hypochlorous acid, calcium hypochlorite, or sodium hypochlorite), other disinfectants like ozone, hydrogen peroxide, and ultraviolet (UV) light can be used.

Chlorine acts as a powerful disinfectant, exerting a toxic action on microorganisms. It also functions as an oxidant on non-degraded organic matter and certain minerals. It is important to note that while sterilization is achieved, chlorine does not necessarily destroy all saprophytes (organisms that live on dead organic matter).

2. Treatment with Ozone (O₃)

Ozone (O₃) is formed by the union of an oxygen molecule (O₂) with a free oxygen atom (O). This free atom is typically the result of oxygen dissociation caused by an electric discharge.

Ozone is one of the most powerful oxidants available (second only to fluoride). It effectively oxidizes iron, manganese, and other heavy metals. It destroys viruses, bacteria, and fungi, and is used to break down complex substances like detergents and pesticides.

Ozone generators are used, which pass an electric current through air or pure oxygen and inject the resulting ozone into the water being treated. Ozone helps adjust turbidity and color, and metabolizes non-biodegradable or difficult-to-remove substances. Furthermore, ozone treatment can clean the air within the facility and improve overall water quality.